Add Qdrant to USERS.md (facebook#12072)

Summary: Pull Request resolved: facebook#12072

Reviewed By: cbi42

Differential Revision: D51398080

Pulled By: ajkr

fbshipit-source-id: 1043f2b012bd744e9c53c638e1ba56a3e0392e11

USERS.md

@@ -152,6 +152,9 @@ LzLabs is using RocksDB as a storage engine in their multi-database distributed
 ## ArangoDB
 [ArangoDB](https://www.arangodb.com/) is a native multi-model database with flexible data models for documents, graphs, and key-values, for building high performance applications using a convenient SQL-like query language or JavaScript extensions. It uses RocksDB as its storage engine.
 
+## Qdrant
+[Qdrant](https://qdrant.tech/) is an open source vector database, it [uses](https://qdrant.tech/documentation/concepts/storage/) RocksDB as its persistent storage.
+
 ## Milvus
 [Milvus](https://milvus.io/) is an open source vector database for unstructured data. It uses RocksDB not only as one of the supported kv storage engines, but also as a message queue.